Control StructuresLecture 3

Instructors: Fu-Chiung Cheng

(鄭福炯 )Associate Professor

Computer Science & EngineeringTatung University

email: cheng@cse.ttu.edu.twhttp:// www.cse.ttu.edu.tw/~cheng

Contents: Control Structures

• DecisionUsing if and if...elseNested if StatementsShortcut if StatementsUsing switch Statements

• RepetitionLooping: for, while, and doNested loopsUsing break and continue

Decisions

if Statements

switch Statements

Shortcut if Statements

if Statements

Format:Format:if (booleanExpression) if (booleanExpression) { {

statement(s);statement(s);}}

Example:Example:if ((i >= 0) && (i <= 10)) if ((i >= 0) && (i <= 10)) System.out.println("i is between 0 and 10");System.out.println("i is between 0 and 10");

The if...else Statement Format:Format:if (booleanExpression) if (booleanExpression) { { statement(s)-for-the-true-case;statement(s)-for-the-true-case;}}else else {{ statement(s)-for-the-false-case;statement(s)-for-the-false-case;}}

if...else Example

if (radius >= 0)if (radius >= 0){ { area = radius*radius*PI;area = radius*radius*PI; System.out.println("The area for the System.out.println("The area for the circle of radius " + radius + " is " + area);circle of radius " + radius + " is " + area);}}elseelse{{ System.out.println("Negative input");System.out.println("Negative input");}}

Nested if Statements

Example 3.1: Using Nested if Example 3.1: Using Nested if StatementsStatements

This program reads in year and loan This program reads in year and loan amount and computes the monthly amount and computes the monthly pay and total pay. The interest rate is pay and total pay. The interest rate is determined by year. determined by year.

TestIfElseTestIfElse Run

Shortcut if Statements

if (x > 0) y = 1if (x > 0) y = 1else y = -1;else y = -1;

is equivalent tois equivalent to

y = (x > 0) ? 1 : -1;y = (x > 0) ? 1 : -1;

switch Statements

switch (year)switch (year){ { case 7: interestRate = 7.25;case 7: interestRate = 7.25; break;break; case 15: interestRate = 8.50;case 15: interestRate = 8.50; break;break; case 30: interestRate = 9.0;case 30: interestRate = 9.0; break;break; default: System.out.println(default: System.out.println( "Wrong Year, enter 7, 15, or 30");"Wrong Year, enter 7, 15, or 30");}}

switch Statement Flow Chart

Repetitions

for Loops

while Loops

do Loops

break and continue

for Loops Format:Format:

for (control-variable-initializer;for (control-variable-initializer; continue-condition; adjustment-statement)continue-condition; adjustment-statement)

{{ //loop body;//loop body;

}}

Example:Example:int i;int i;for (i = 0; i<100; i++)for (i = 0; i<100; i++){{

System.out.println("Welcome to Java!” + i); System.out.println("Welcome to Java!” + i); }}

// for (int i = 0; i<100; i++) // for (int i = 0; i<100; i++)

for Loop Flow Chart

for Loop Examples

Examples for using the for loop:

Example 3.2: TestSum.java

TestSumTestSum

TestMulTableTestMulTable

Example 3.3: TestMulTable.java

Run

Run

while Loops Format:Format:

while (continue-condition) while (continue-condition) {{ // loop-body;// loop-body;}}

ExampleExample 3.4: TestWhile.java3.4: TestWhile.java

TestWhileTestWhile Run

while Loop Flow Chart

do Loops Format:Format:

dodo{{ //loop body;//loop body;} while (continue-condition)} while (continue-condition)

do Loop Flow Chart

The break Keyword

The continue Keyword

Using break and continue

Examples for using the break and continue keywords:

Example 3.5: TestBreak.java

Example 3.6: TestContinue.java

TestBreakTestBreak

TestContinueTestContinue

Run

Run